The US military claimed in the note that Dr Izmerly, a distinguished chemistry professor arrested after US tanks encircled his villa, had died of "brainstem compression".
Dr Izmerly's sudden death after 10 months in American custody left his family stunned, not least because three weeks earlier they had visited him in the US prison at Baghdad airport. His 23-year-old daughter, Rana, recalled that he had seemed in "good health".
The family commissioned an independent Iraqi autopsy. Its conclusion was unambiguous: Dr Izmerly had died because of a "sudden hit to the back of his head", Faik Amin Baker, the director of Baghdad hospital's forensic department, certified.
The cause of death was blunt trauma. It was uncertain exactly how he died, but someone had hit him from behind, possibly with a bar or a pistol, Dr Baker confirmed yesterday.
"He died from a massive blow to the head. We don't disagree with the coalition's report, but it doesn't explain how he got his injuries in the first place," he told the Guardian.
The apparent murder of a "high-value" detainee, held as part of the search for weapons of mass destruction, is another blow for the Bush administration, still reeling from the Abu Ghraib jail abuse scandal.
Dr Izmerly was on the coalition's original "200 list" of suspects from Saddam Hussein's regime, and his death happened just two weeks after the US military began its own secret inquiry into the prison west of Baghdad. Last Friday the Pentagon admitted it was now investigating eight more suspected murders.
Several prisoners have been found to have died before or during interrogation. They include Major General Abed Hamed Mowhoush, a former commander of Iraq's air defences, who died last November during interrogation at Qaim.
The original US autopsy said he had died of a heart attack. It now appears he was suffocated during interrogation when a CIA officer put him in a sleeping bag and sat on him.
Last night the family of Dr Izmerly were in little doubt he had been murdered in US custody. The reasons for his death were covered up, they believe.
"This was not natural," Rana told the Guardian yesterday, in the first interview given by the family since his death. "The evidence is clear. It suggests the Americans killed him and then tried to hide what they had done. I will hate Americans and British people for the rest of my life. You are democrats. You said you were coming to bring democracy, and yet you kill my father. By accepting your governments, you accept what they do here in Iraq.
"You offer no proof that he did something wrong, you refuse him a lawyer and then you kill him. Why?"
Dr Izmerly does not appear to be among the cases under the review announced by the US defence department last week.
The death certificate provided by the coalition, which is almost entirely blank, fails to explain how he got a fracture in his skull, or the small cut above his left eye. The scientist is merely a number, 1909.
Asked to explain how he had died, a coalition spokesman said last night: "There are several investigations currently under way into the issue of detainee abuse. It is inappropriate for us to comment on ongoing investigations."
The professor's 60-year-old widow, Sahera Abdullah, said she had received no satisfactory explanation of why he had been arrested in the first place. His study at his villa in the Baghdad suburb of al-Khadra had burned down during a shootout between US soldiers and Saddam's paramilitaries, the Fedayeen, during last year's war, she said.
Soon afterwards, on April 25, US tanks encircled the house. Marines kicked in the front door and then ransacked the home, carting off books, papers, computers and family photographs. Mrs Izmerly said: "They stayed for a day. I offered them tea and coffee. They seemed surprised."
The next day Dr Izmerly gave himself up. The family admits that he had met Saddam the previous year, but says he was part of a group of academics summoned to meet the president. The family admits that the price of his going to international scientific conferences was to pass information to the mukhabarat, the secret police.
The first Red Cross letter arrived last May, but the family was still no wiser as to where the US was holding him. After six months, they were allowed to drop off some winter clothes at al-Taji, a US military base north of Baghdad. There were three telephone calls. But their attempts to visit him got nowhere.
Finally, Rana and her elder sister, Nuha, 27, and brother, Ashraf, 21, discovered that their father was being kept at the US base at Baghdad international airport. On January 11, they managed to see him.
A US officer, known as Mr Jakey, drove them blindfolded on a zigzagging route through the camp. They were taken to an empty tourist villa. Her father emerged from a side door. They gave him some sweets. "When I saw him his health was good. He was normal. He was dressed in the clothes we sent him earlier," Rana said. "But he refused to talk about what had happened to him in custody. I asked the Americans why they had arrested him. They told me simply, 'He is a witness'."
The Red Cross visited him on January 19. On February 17, the organisation informed the family that he was dead. "I went to the morgue in the hospital and found him in a black US body bag," Ashraf said yesterday. "There was a cut on his head behind his right ear. It was hard to miss."
It was discovered that US doctors had made a 20cm incision in his skull, apparently in an attempt to save his life after the initial blow.
The family presented its autopsy findings to an Iraqi judge. "He told us, 'You can't do anything to the coalition. What happened is history,'" Ashraf said.
Yesterday, as darkness fell around the scientist's home, the family showed some of their father's belongings returned from the jail - a few Red Cross letters, a bag of clothes and a framed photo.
But there also was the legacy of emotion - of a kind now common across Iraq, and swelling into a storm. "I won't allow myself to rest until I have got revenge for him," Rana said.